Anomalous butterfly-shaped magnetoresistance loops in the alloy Tb4LuSi3

The materials exhibiting magnetic-field-induced first-order magnetic transitions are usually characterized by irreversibility in magnetoresistance (MR). The envelope curve in such cases has been known to lie below the virgin curve in MR versus magnetic-field plots as a consequence of relatively lower electrical resistivity of ferromagnetically aligned high-field phase attained after first-order transition. Here, we report a deviation from this general behavior of MR loop for an alloy, Tb4LuSi3, at low temperatures (<< 20 K) in the magnetically ordered state in the sense that the virgin curve lies below the envelope curve. Such an anomalous curve reveals unexpected domination of higher resistive high-field phase in electrical conduction. The observed features thus bring out an unusual electronic phase separation involving a complex high-field phase.